Morphological and optical characterization of post-annealed ZnO films prepared by sol-gel method

Transparent zinc oxide (ZnO) films have been prepared by sol-gel method using spin coating method on quartz glass from 0.5M zinc acetate 2-methoxyethonal solution, and using monoethanolamine(MEA) as stabilizer. The as-prepared samples were heat-treated at 550 degrees C for 90min in air, oxygen and vacuum ambient, respectively. XRD patterns show that the prepared samples exhibit wurtzite structure, the sample annealed in O-2 has best crystalline quality and biggest degree of preferential orientation of (0O2) plane, and the sample annealed in vacuum nearly has,no preferential orientation. It can be found from AFM images that surface roughness of the three films are: Vacuum > air > O-2. The sample annealed in O-2 has rod-like and uniform particles, the sample annealed in air with ball-like particles and sample heat treated under vacuum ambient with ball-like uniform particles. PL analysis tells that vacuum atmosphere leads to more oxygen vacancy (VO) and zinc excess, however annealed in O-2 can decrease the oxygen vacancy (VO) and zinc excess obviously. The band gap of prepared ZnO films is about 3.3eV from PL spectra. Through analyze the UV-Vis result, it can be found that the surface morphology does influence the absorptance. Generally speaking, the annealed ambient influences the intrinsic defect and extrinsic defect, and then influence the properties of prepared ZnO films.